Making the most of alarm signals: the adaptive value of individual discrimination in an alarm context

The value of individual discrimination is straightforward for many signal contexts, such as with contact or isolation calls, territorial marks, or status announcements. In contrast, the value of individual discrimination is less straightforward for alarm signals, and it is not yet known how or under what circumstances individual discrimination would be beneficial in an alarm context. One proposed mechanism is that receivers may discriminate individual signalers and respond differently based on the signaler's reliability, and that this may allow the receivers to optimize their antipredator behavior. To evaluate this mechanism, I constructed a dynamic model to test the fitness outcomes of 5 receiver response strategies under varying environmental, life history, and social conditions. The individual discrimination strategy yielded the highest fitness under the widest range of conditions, and the difference was substantial except in cases of very low predation pressure and high signaler accuracy. The adaptive value of individual discrimination of alarm signals may thus be a general phenomenon in nature and may provide evolutionary pressure for animals to increase their discrimination abilities. For species that use alarm signals nepotistically, the value of individual discrimination could provide selective pressure for the evolution of individual signatures in alarms and may help explain why the alarm signals of many species are so individualistic. Copyright 2011, Oxford University Press.